Television receiver automatic frequency control system

Abstract

A television receiver includes a tuner, IF amplifier, video and audio processing circuitry and deflection circuits. Two quadrature detectors are driven from the IF amplifier, one tuned to the sound IF carrier frequency and the other tuned to the picture IF carrier frequency. A combining circuit accepts only negative-going error voltages from the first detector and only positive-going error voltages from the second detector to produce an AFC with a response curve defined by the sound IF frequency at one end and the picture IF frequency at the other end. The output of the combining circuit supplies a voltage controllable oscillator in the tuner.

What is claimed is: 
     
       1. A television receiver for receiving television signals having RF picture and sound carriers spaced a predetermined distance apart comprising: means translating said received television signals including; a tuner having a controllable oscillator, a mixer heterodyning the output signal of the oscillator with said received television signal to convert said RF carriers into picture and sound IF carriers of fixed intermediate frequencies, and an IF amplifier; and AFC means coupled between said IF amplifier and said controllable oscillator for producing correction voltages for said oscillator, said AFC means comprising a first detector detecting signals at frequencies corresponding to said picture IF carrier frequency, a second detector detecting signals at frequencies corresponding to said sound IF carrier frequency and combining means supplied from said first and second detectors for producing a composite AFC amplitude versus frequency response characterized by portions of opposite polarity between limits defined by said picture and sound IF carrier frequencies. 
     
     
       2. A television receiver as set forth in claim 1, wherein said response curve has detection slopes at frequencies corresponding to said picture and sound IF carriers and substantially equal size opposite polarity portions. 
     
     
       3. A wide range AFC circuit including separate picture and sound detection means, for use in a television receiver, exhibiting an amplitude versus frequency response characteristic having two portions and producing a first polarity correction voltage for signal frequencies falling in one of said portions and a second polarity correction voltage for signal frequencies falling in the other of said portions; said wide range being bounded by detection slopes at the nominal IF frequencies of the sound and picture IF carriers of a translated television signal. 
     
     
       4. A wide range AFC circuit as claimed in claim 3, including combining means coupled to said first and said second detector means for combining portions of their respective output voltages. 
     
     
       5. A wide range AFC circuit as claimed in claim 4, wherein said combining means accepts output voltages of one polarity from said first detector means and output voltages of opposite polarity from said second detector means. 
     
     
       6. A wide range AFC circuit as claimed in claim 4, wherein the response characteristics of said first and second detector means are similar with steep detection slopes at their respective detection frequencies, the different polarity portions of said wide range response characteristic being substantially similar in size and shape. 
     
     
       7. A wide range AFC circuit as claimed in claim 5, wherein said first and said second detector means each include a quadrature detector. 
     
     
       8. A wide range AFC circuit as claimed in claim 5, wherein said combining means comprises a pair of semiconductor circuit elements for amplifying said opposite polarity portions of the outputs of said detector means. 
     
     
       9. A wide range AFC circuit as claimed in claim 6, wherein said translated television signal is an NTSC television signal and said wide range comprises 4.5 MHz.